U.S. patent application number 14/440649 was filed with the patent office on 2015-10-08 for radio resource setting method, base station, radio resource setting system, and non-transitory computer readable medium.
The applicant listed for this patent is NEC CORPORATION. Invention is credited to Takahiro Nobukiyo, Daisuke Ohta.
Application Number | 20150289263 14/440649 |
Document ID | / |
Family ID | 50684263 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150289263 |
Kind Code |
A1 |
Ohta; Daisuke ; et
al. |
October 8, 2015 |
RADIO RESOURCE SETTING METHOD, BASE STATION, RADIO RESOURCE SETTING
SYSTEM, AND NON-TRANSITORY COMPUTER READABLE MEDIUM
Abstract
The method is a method of setting radio resources which a pico
base station (100) and a macro base station (200) can use for
wireless communication with a terminal, and includes obtaining
loads the pico base station (100) and the macro base station (200),
calculating a first delay index of the pico base station using the
load of the pico base station (100), calculating using the load of
the macro base station (200) a second delay index of the macro base
station (200) in case where the macro base station (200) has set
radio resources whose use is limited, and calculating a ratio of
the radio resources whose use is limited by the macro base station
(200) based on the first and second delay indices, and setting the
radio resources whose use is limited in the second communication
area using the ratio of the radio resources whose use is
limited.
Inventors: |
Ohta; Daisuke; (Tokyo,
JP) ; Nobukiyo; Takahiro; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC CORPORATION |
Minato-ku, Tokyo |
|
JP |
|
|
Family ID: |
50684263 |
Appl. No.: |
14/440649 |
Filed: |
June 24, 2013 |
PCT Filed: |
June 24, 2013 |
PCT NO: |
PCT/JP2013/003932 |
371 Date: |
May 5, 2015 |
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 28/16 20130101;
H04W 84/042 20130101; H04W 72/0446 20130101; H04W 16/04 20130101;
H04W 24/08 20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04W 24/08 20060101 H04W024/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2012 |
JP |
2012-246962 |
Claims
1. A radio resource setting method for, when there are a first
communication area managed by a first base station and a second
communication area including at least part of the first
communication area and managed by a second base station, setting
radio resources that the first and second base stations can use for
wireless communication with a terminal, the radio resource setting
method comprising: obtaining loads of the first communication area
and the second communication area; calculating a first delay index
of the first communication area using the load of the first
communication area; calculating using the load of the second
communication area a second delay index of the second communication
area in case where the radio resources whose use is limited in the
second communication area have been set; calculating a ratio of
radio resources whose use is limited in the second communication
area based on the first delay index and the second delay index; and
setting the radio resources whose use is limited in the second
communication area using the ratio of the radio resources whose use
is limited.
2. The radio resource setting method according to claim 1, further
comprising, upon calculation of the ratio of the radio resources
whose use is limited, calculating a relative delay index that is a
difference between or a ratio of the first delay index and the
second delay index, wherein the ratio of the radio resources whose
use is limited is updated to a value that is a predetermined
addition step larger than a latest ratio of the radio resources
whose use is limited when the relative delay index is larger than a
first threshold of the relative delay index, and is updated to a
value that is a predetermined subtraction step smaller than the
latest ratio of the radio resources whose use is limited when the
relative delay index is smaller than a second threshold of the
relative delay index.
3. The radio resource setting method according to claim 1, wherein
the ratio of the radio resources whose use is limited is calculated
using the first delay index, the second delay index and a
difference between or a ratio of the first delay index and the
second delay index.
4. The radio resource setting method according to claim 1, wherein
the load is a band use ratio.
5. The radio resource setting method according to claim 1, wherein
the load is a number of terminals.
6. The radio resource setting method according to claim 1, wherein
the load is a delay time of the terminal.
7. The radio resource setting method according to claim 1, wherein
the load is a throughput of the terminal.
8. The radio resource setting method according to claim 1, wherein
the second base station calculates the ratio of the radio resources
whose use is limited in the second communication area.
9 The radio resource setting method according to claim 1, wherein
the first base station calculates the ratio of the radio resources
whose use is limited in the second communication area, and notifies
the second base station of a result of the calculation.
10. A base station that performs wireless communication with a
terminal in a second communication area that is at least one of a
neighboring communication area of a first communication area or a
communication area including part of the first communication area,
the base station comprising: a load measuring unit that measures a
load of the second communication area; and an allocation ratio
resource setting unit that calculates a first delay index of the
first communication area using the load of the first communication
area notified from an other base station that manages the first
communication area, calculating using the load of the second
communication area a second delay index of the second communication
area in case where the radio resources whose use is limited in the
second communication area have been set, and calculating a ratio of
radio resources whose use is limited in the second communication
area based on the first delay index and the second delay index.
11. The base station according to claim 10, wherein the allocation
radio resource setting unit calculates a relative delay index that
is a difference between or a ratio of the first delay index and the
second delay index, and updates the ratio of the radio resources
whose use is limited, to a value that is a predetermined addition
step larger than a latest ratio of the radio resources whose use is
limited when the relative delay index is larger than a first
threshold of the relative delay index, and updates the ratio of the
radio resources whose use is limited, to a value that is a
predetermined subtraction step smaller than the latest ratio of the
radio resources whose use is limited when the relative delay index
is smaller than a second threshold of the relative delay index.
12. The base station according to claim 10, wherein the allocation
radio resource setting unit calculates the ratio of the radio
resources whose use is limited using the first delay index, the
second delay index and a difference between or a ratio of the first
delay index and the second delay index.
13. The base station according to claim 10, wherein the load is a
band use ratio.
14. The base station according to claim 10, wherein the load is a
number of terminals.
15. The base station according to claim 10, wherein the load is a
delay time of the terminal.
16. The base station according to claim 10, wherein the load is a
throughput of the terminal.
17. A base station that, when there is a second communication area
that is at least one of a neighboring communication area of a first
communication area or a communication area including part of the
first communication area, performs wireless communication with a
terminal in the first communication area, the base station
comprising: a load measuring unit that measures a load of the first
communication area; and a priority resource requesting unit that
calculates a first delay index of the first communication area
using the load of the first communication area, calculating using
the load of the second communication area transmitted from an other
base station that manages the second communication area a second
delay index of the second communication area in case where the
radio resources whose use is limited in the second communication
area have been set, and calculating a ratio of radio resources
whose use is limited in the second communication area based on the
first delay index and the second delay index, and notifying the
other base station that manages the second communication area of a
result of the calculation.
18. The base station according to claim 17, wherein the priority
resource requesting unit calculates a relative delay index that is
a difference between or a ratio of the first delay index and the
second delay index, and updates the ratio of the radio resources
whose use is limited, to a value that is a predetermined addition
step larger than a latest ratio of the radio resources whose use is
limited when the relative delay index is larger than a first
threshold of the relative delay index, and updates the ratio of the
radio resources whose use is limited, to a value that is a
predetermined subtraction step smaller than the latest ratio of the
radio resources whose use is limited when the relative delay index
is smaller than a second threshold of the relative delay index.
19. The base station according to claim 17, wherein the priority
resource requesting unit calculates the ratio of the radio
resources whose use is limited using the first delay index, the
second delay index and a difference between or a ratio of the first
delay index and the second delay index.
20. The base station according to claim 17, wherein the load is a
band use ratio.
21. The base station according to claim 17, wherein the load is a
number of terminals.
22. The base station according to claim 17, wherein the load is a
delay time of the terminal.
23. The base station according to claim 17, wherein the load is a
throughput of the terminal.
24. A radio resource setting system that, when there are a first
communication area managed by a first base station and a second
communication area including at least part of the first
communication area and managed by a second base station, sets radio
resources that the first and second base stations can use for
wireless communication with a terminal, wherein the radio resource
setting system is configured to: obtain loads of the first
communication area and the second communication area; calculate a
first delay index of the first communication area using the load of
the first communication area; calculate using the load of the
second communication area a second delay index of the second
communication area in case where the radio resources whose use is
limited in the second communication area have been set; calculate a
ratio of the radio resources whose use is limited in the second
communication area based on the first delay index and the second
delay index; and set the radio resources whose use is limited in
the second communication area using the ratio of the radio
resources whose use is limited.
25. A non-transitory computer readable medium having stored thereon
a program that is executed by a computer of a base station that
performs wireless communication with a terminal in a second
communication area that is at least one of a neighboring
communication area of a first communication area or a communication
area including part of the first communication area, the program
causing the computer to execute: obtaining a load of the second
communication area; calculating a first delay index of the first
communication area using a load of the first communication area
notified from an other base station that manages the first
communication area; calculating using the load of the second
communication area a second delay index of the second communication
area in case where the radio resources whose use is limited in the
second communication area have been set; and calculating a ratio of
the radio resources whose use is limited in the second
communication area based on the first delay index and the second
delay index.
Description
TECHNICAL FIELD
[0001] The present invention relates to an allocation radio
resource setting method and, more particularly, relates to an
allocation radio resource setting method of suppressing an
interference with a neighboring cell.
BACKGROUND ART
[0002] A wireless communication system such as LTE (Long Term
Evolution) standardized by 3GPP (Third Generation Partnership
Project) assumes that a plurality of base stations are located.
Each base station used for the wireless communication system
communicates with terminals (mobile stations) in a communication
area (referred to as a cell below) of each base station. Further, a
base station can divide a cell into a plurality of regions when an
antenna has directionality. These divided regions are referred to
as sector cells. Cells described below include not only normal
cells but also sector cells.
[0003] According to LTE, the same communication band is usually
used between neighboring cells. Hence, a terminal (referred to as
an edge terminal below) positioned at a boundary between cells
receives a strong interference from a neighboring cell
irrespectively of in uplink or in downlink. To deal with such a
problem, an interference management technique which is called ICIC
(Inter Cell Interference Coordination) and suppresses an
interference between neighboring cells by setting a priority band
which enables a terminal in a corresponding cell to preferentially
perform communication, and, in each cell, limiting allocation radio
resources of a priority band of a neighboring cell for a terminal
is known. It is conceived that radio resources are limited by
excluding a priority band from an allocation target or reducing
transmission power of this priority band when the priority band is
notified from the neighboring cell.
[0004] As a method of setting a priority band, a technique which is
called FFR (Fractional Frequency Reuse) and performs fractional
frequency reuse such that a priority band does not overlap between
cells is known (Non-Patent Literature 1). Further, as a priority
band notifying method, LOAD INFORMATION is standardized according
to LTE. For example, RNTP (Relative Narrowband TX Power) is defined
in downlink of LTE, and HIT (High Interference Indication) is
defined in uplink (Non-Patent Literature 2).
[0005] Further, as a counter measure for an increase in a traffic
amount in recent years, a heterogeneous network in which cells of
various sizes are provided by introducing base stations (small cell
base stations) of low transmission power in hot spots in addition
to conventional macro base stations in a mixed fashion is gaining
attention. However, a cell boundary area expands as the number of
cells increases, and therefore an inter-cell interference is
regarded as a problem.
[0006] According to 3GPP Release 10, eICIC (enhanced ICIC) has been
studied as an interference management technique, and an ABS (Almost
Blank Subframe) has been standardized (Non-Patent Literature 3).
eICIC is also referred to as time domain ICIC, and a base station
which has set ABSs stops transmission in the ABSs through a control
channel (PDCCH: Physical Downlink Control Channel) and a data
channel (PDSCH: Physical Downlink Shared Channel) in downlink. A
subframe is a radio resource allocation unit time. Thus, the SINR
of a terminal in a neighboring cell substantially improves in the
ABS, and an increase in throughputs of terminals is expected.
CITATION LIST
Non Patent Literature
[0007] NPL 1: Bin Fan et al., "A Dynamic Resource Allocation Scheme
Based on Soft Frequency Reuse for OFDMA Systems", IEEE 2007
International Symposium on Microwave, Antenna, Propagation and EMC
Technologies for Wireless Communications, pp. 121-125, August
2007
[0008] NPL 2: 3GPP TS 36.423 V9.0.0 (2009-09), 3GPP TSG RAN E-UTRAN
X2AP, pp. 16-17, p. 29, p. 49, September 2009
[0009] NPL 3: 3GPP TS 36.300 V10.6.0 (2011-12), 3GPP TSG RAN E-UTRA
and E-UTRAN Overall description Stage 2 (Release 10), p. 116,
December 2011
SUMMARY OF INVENTION
Technical Problem
[0010] A macro base station which has set ABSs cannot allocate
radio resources in the ABSs. Therefore, the throughputs of
terminals of the macro base station deteriorate. Therefore, there
is a problem that, when an ABS ratio is a fixed value, fairness
between throughputs of all terminals of a wireless communication
system is substantially lost.
[0011] FIG. 14 illustrates a 5% value of throughputs of macro
terminals, pico terminals and all terminals before eICIC is applied
and when eICIC is applied to three patterns of ABS ratios.
[0012] When the ABS ratio with respect to traffic loads of the
macro base station and the pico base station before eICIC is
applied is too small, throughputs of pico terminals hardly improve.
Meanwhile, when the ABS ratio is too large, the throughputs of the
terminals of the pico base station improve. However, the
throughputs of the terminals of the macro base station
substantially deteriorate, and therefore a balance between the
throughputs of the terminals of the macro base station and the pico
base station is lost. Particularly when throughputs of edge
terminals of the macro base station deteriorate, the 5% value of
the throughputs of all terminals deteriorates. Therefore, the
fairness between the throughputs of the terminals is lost.
[0013] To solve the above problem, an object of the present
invention is to provide a radio resource setting method, a base
station, a radio resource setting system and a program which can
improve fairness between throughputs of all terminals.
Solution to Problem
[0014] A radio resource setting method according to a first aspect
of the present invention is a radio resource setting method for,
when there are a first communication area managed by a first base
station and a second communication area including at least part of
the first communication area and managed by a second base station,
setting radio resources that the first and second base stations can
use for wireless communication with a terminal, and includes:
obtaining loads of the first communication area and the second
communication area; calculating a first delay index of the first
communication area using the load of the first communication area;
calculating using the load of the second communication area a
second delay index of the second communication area in case where
the radio resources whose use is limited in the second
communication area have been set; calculating a ratio of radio
resources whose use is limited in the second communication area
based on the first delay index and the second delay index; and
setting the radio resources whose use is limited in the second
communication area using the ratio of the radio resources whose use
is limited.
[0015] A base station according to a second aspect of the present
invention is a base station that performs wireless communication
with a terminal in a second communication area that is at least one
of a neighboring communication area of a first communication area
or a communication area including part of the first communication
area, and includes: a load measuring unit that measures a load of
the second communication area; and an allocation radio resource
setting unit that calculates a first delay index of the first
communication area using the load of the first communication area
notified from an other base station that manages the first
communication area, calculates using the load of the second
communication area a second delay index of the second communication
area in case where the radio resources whose use is limited in the
second communication area have been set, and calculates a ratio of
radio resources whose use is limited in the second communication
area based on the first delay index and the second delay index.
[0016] A radio resource setting system according to a third aspect
of the present invention is a radio resource setting system that,
when there are a first communication area managed by a first base
station and a second communication area including at least part of
the first communication area and managed by a second base station,
sets radio resources that the first and second base stations can
use for wireless communication with a terminal, and is configured
to: obtain loads of the first communication area and the second
communication area; calculate a first delay index of the first
communication area using the load of the first communication area;
calculate using the load of the second communication area a second
delay index of the second communication area in case where the
radio resources whose use is limited in the second communication
area have been set; calculate a ratio of the radio resources whose
use is limited in the second communication area based on the first
delay index and the second delay index; and set the radio resources
whose use is limited in the second communication area using the
ratio of the radio resources whose use is limited.
[0017] A program according to a fourth aspect of the present
invention is a program that is executed by a computer of a base
station that performs wireless communication with a terminal in a
second communication area that is at least one of a neighboring
communication area of a first communication area or a communication
area including part of the first communication area, and causes the
computer to execute: obtaining a load of the second communication
area; calculating a first delay index of the first communication
area using a load of the first communication area notified from an
other base station that manages the first communication area;
calculating using the load of the second communication area a
second delay index of the second communication area in case where
the radio resources whose use is limited in the second
communication area have been set; and calculating a ratio of the
radio resources whose use is limited in the second communication
area based on the first delay index and the second delay index.
Advantageous Effects of Invention
[0018] The present invention can provide a radio resource setting
method, a base station, a radio resource setting system and a
program which can improve fairness between throughputs of all
terminals.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a configuration diagram of a wireless
communication system according to a first embodiment.
[0020] FIG. 2 is a configuration diagram of a pico base station and
a macro base station according to the first embodiment.
[0021] FIG. 3 is a view illustrating a method where the macro base
station sets radio resources whose use is limited according to the
first embodiment.
[0022] FIG. 4 is a configuration diagram of a terminal according to
the first embodiment.
[0023] FIG. 5A is a view illustrating a method where the macro base
station calculates a ratio of radio resources whose use is limited
according to the first embodiment.
[0024] FIG. 5B is a view illustrating a method where the macro base
station calculates a ratio of radio resources whose use is limited
according to the first embodiment.
[0025] FIG. 6 is a configuration diagram of a macro base station
according to a second embodiment.
[0026] FIG. 7 is a view illustrating a method where the macro base
station calculates a ratio of radio resources whose use is limited
according to the second embodiment.
[0027] FIG. 8 is a configuration diagram of a macro base station
according to a third embodiment.
[0028] FIG. 9 is a view illustrating a method where the macro base
station sets radio resources whose use is limited according to the
third embodiment.
[0029] FIG. 10 is a view illustrating a method where the macro base
station calculates a ratio of radio resources whose use is limited
according to the third embodiment.
[0030] FIG. 11 is a configuration diagram of a pico base station
and a macro base station according to a fourth embodiment.
[0031] FIG. 12 is a view illustrating a method where the pico base
station requests radio resources whose use is limited according to
the fourth embodiment.
[0032] FIG. 13 is a view illustrating a method where the macro base
station sets radio resources whose use is limited according to the
fourth embodiment.
[0033] FIG. 14 is a view illustrating a problem caused when eICIC
is applied.
DESCRIPTION OF EMBODIMENTS
First Embodiment
ABS Ratio is Updated by Predetermined Step According to Load
[0034] Next, an embodiment of the present invention will be
described in detail with reference to the drawings.
[0035] [Explanation of Configuration]
[0036] FIG. 1 illustrates a configuration of a wireless
communication system 10 according to the first embodiment of the
present invention. The present invention is applied to downlink of
LTE in the wireless communication system 10. The wireless
communication system 10 includes pico base stations 100-1 and
100-2, macro base stations 200-1 and 200-2, and a plurality of
terminals 300-P1-1, 300-P1-2, 300-P2-1, 300-P2-2, 300-M1-1,
300-M1-2, 300-M2-1 and 300-M2-2. An example where the wireless
communication system 10 includes two macro base stations and two
pico base stations will be described with reference to FIG. 1.
However, the wireless communication system 10 may include two or
more base stations. Further, the wireless system communication 10
may include a greater number of terminals than the number of
terminals illustrated in FIG. 1. M represents an initial letter of
Macro, and P represents an initial letter of Pico. In this regard,
a terminal 300-P1-X is connected to the pico base station 100-1.
Further, a terminal 300-M1-Y is connected to the macro base station
200-1. X and Y represent arbitrary indices for allowing each base
station to identify a terminal.
[0037] Common matters between respective pico base stations and
between respective macro base stations will be described below to
read "a pico base station 100 . . . " and "a macro base station 200
. . . ", respectively. Similarly, common matters between respective
terminals connected to a pico base station and between respective
terminals connected to a macro base station will be described to
read "a pico terminal 300-P . . . " and "a macro terminal 300-M . .
. ", respectively. Further, common matters irrespectively of base
stations to connect to will be described to read "a terminal 300 .
. . ".
[0038] The pico base stations 100-1 and 100-2 and the macro base
stations 200-1 and 200-2 can communicate with each other through a
communication line NW. Further, each pico base station 100 and each
macro base station 200 each can manage a plurality of communication
areas (cells). In the present embodiment, an example where each
pico base station 100 and each macro base station 200 each manage
one communication area will be described in the present
embodiment.
[0039] The pico base station 100 is a low transmission power base
station, and includes a narrower communication area than that of
the macro base station 200. The communication area of each pico
base station 100 is a communication area at least part of which is
included in the communication area of each macro base station
200.
[0040] Each pico base station 100 performs wireless communication
with the terminal 300-P in the communication area managed by the
pico base station 100. Each pico base station 100 can
simultaneously execute wireless communication with a plurality of
terminals 300-P, respectively.
[0041] Each macro base station 200 performs wireless communication
with the terminal 300-M in a communication area formed by
subtracting the communication area managed by the pico base station
100 from the communication area managed by the macro base station
200. Each macro base station 200 can simultaneously execute
wireless communication with a plurality of terminals 300-M,
respectively.
[0042] Each pico base station 100 and each macro base station 200
each include an information processing apparatus which is not
illustrated. The information processing apparatus includes a
central processing unit (CPU) and a storage device (a memory and a
hard disk drive (HDD)) which are not illustrated. Each pico base
station 100 and each macro base station 200 are each configured to
realize functions described below when the CPU executes a program
stored in the storage device.
[0043] Each terminal 300 is a mobile telephone terminal. In
addition, each terminal 300 may be a personal computer, a PHS
(Personal Handyphone System) terminal, a PDA (Personal Data
Assistance or Personal Digital Assistant), a smartphone, a car
navigation terminal, a game terminal or the like.
[0044] Each terminal 300 includes a CPU, a storage device (memory),
an input device (key buttons and a microphone) and an output device
(a display and a speaker). Each terminal 300 is configured to
realize functions described below when the CPU executes a program
stored in the storage device.
[0045] FIG. 2 is a block diagram illustrating the functions of each
pico base station 100 and each macro base station 200 in the
wireless communication system 10 configured as described above. The
functions will be described using the pico base station 100-1 as a
pico base station and the macro base station 200-1 as a macro base
station. Although not illustrated in FIG. 2, functions of the pico
base station 100-2 are the same as the functions of the pico base
station 100-1. Similarly, functions of the macro base station 200-2
are the same as the functions of the macro base station 200-1.
[0046] The pico base station 100-1 includes a base station
operating unit 101, a reference signal generating unit 102, a load
measuring unit 103, a transmitting buffer 104 and a scheduler
105.
[0047] The base station operating unit 101 has a function of
transmitting and receiving radio signals to and from each terminal
300-P1 which is being connected with the pico base station 100-1, a
function of notifying each terminal 300-P1 of an allocation band
used to transmit and receive radio signals, scheduling information
such as an MCS (Modulation and Coding Scheme) Index and setting
information of transmission power, and a function of notifying each
terminal 300-P1 of a report timing of CSI (Channel State
Information) such as a CQI (Channel Quarity Indicator). Further,
the base station operating unit 101 includes a surrounding base
station list in which information used to identify the macro base
station 200-1 and other surrounding macro base stations 200-k
(k.noteq.1) is described, and has a function of communicating with
surrounding base stations through the communication line NW, and a
function of holding ABS setting information (ABS Status) notified
from the surrounding base stations. However, these configurations
and operations are known and therefore will not be described.
[0048] The reference signal generating unit 102 has a function of
generating a reference signal which the terminal 300 uses to
measure channel quality with respect to the pico base station
100-1. The reference signal generating unit 102 transmits a
generated signal to each terminal 300 through the base station
operating unit 101.
[0049] The load measuring unit 103 has a function of measuring a
load of the pico base station 100-2 per predetermined cycle, and
notifying the surrounding base stations including at least the
macro base station 200-1 of information of the measured load
through the base station operating unit 101. In the present
embodiment, the load is a PRB (Physical Resource Block) use ratio.
The PRB is a radio band allocation unit.
[0050] The transmitting buffer 104 has a function of accumulating
transmission data which arrives through the communication line NW
and is addressed to each terminal 300-P, and information which is
used to transmit the transmission data.
[0051] The scheduler 105 has a function of determining transmission
power, a frequency band and a MCS Index allocated per terminal
300-P, based on a size of transmission data accumulated in the
transmitting buffer 104 and addressed to each terminal 300-P, the
ABS setting information of the macro base station 200-1 held in the
base station operating unit 101 and the CSI reported from each
terminal 300-P, and transmitting data through the base station
operating unit 101. In the present embodiment, when a current
subframe is an ABS, the scheduler 105 uses a
[0052] CSI of the ABS reported from each terminal 300-P. Further,
when the current subframe is not an ABS (referred to as a Non-ABS
below), the scheduler 105 uses a CSI of a subframe of the Non-ABS
reported from each terminal 300-P.
[0053] The macro base station 200-1 includes a base station
operating unit 201, a reference signal generating unit 202, a load
measuring unit 203, an allocation radio resource setting unit 204,
a transmitting buffer 205 and a scheduler 206.
[0054] The base station operating unit 201 has a function of
transmitting and receiving radio signals to and from each terminal
300-M1 which is being connected with the macro base station 200-1,
a function of determining scheduling information such as an
allocation band and a MCS Index used to transmit and receive the
radio signals, and setting information of transmission power per
terminal 300-M1, and notifying each terminal 300-M1 of the
scheduling information and the setting information, and a function
of notifying each terminal 300-M1 of a report timing of a CSI.
Further, the base station operating unit 201 includes a surrounding
base station list in which information used to identify the pico
base station 100-1, surrounding macro base stations 200-k
(k.noteq.1) and a pico base station 100-k located in a
communication area of each surrounding macro base station 200-k is
described, and has a function of communicating with surrounding
base stations through the communication line NW. However, these
configurations and operations are known and therefore will not be
described.
[0055] The reference signal generating unit 202 has the same
functions as those of the reference signal generating unit 102 of
the pico base station 100-1, and therefore will not be
described.
[0056] The load measuring unit 203 has a function of measuring a
load of the macro base station 200-1 per predetermined cycle, and
notifying the surrounding base stations including at least the pico
base station 100-1 of information of the measured load through the
base station operating unit 201. The allocation radio resource
setting unit 204 uses the load measured by the load measuring unit
203, through the base station operating unit 201.
[0057] The allocation radio resource setting unit 204 has a
function of updating a ratio of radio resources whose use is
limited using load information notified from the pico base station
100-1, the load of the macro base station 200-1 measured by the
load measuring unit 203 and current ABS setting information of the
macro base station 200-1 held in the base station operating unit
201. Further, the allocation radio resource setting unit 204 has a
function of calculating a delay index for determining a delay time
of a terminal of the pico base station 100-1 and a delay index
indicating a delay time of the macro base station 200-1 in case
where radio resources whose use is limited have been set,
respectively, using the updated ratio of the resources whose use is
limited, the load information notified from the pico base station
100-1 and the load of the macro base station 200-1 measured by the
load measuring unit 203.
[0058] Furthermore, the allocation radio resource setting unit 204
has a function of calculating a load index of the macro base
station 200-1 using the load of the macro base station 200-1
measured by the load measuring unit 203 and a size (referred to a
buffer size below) of transmission data which is being buffered in
the transmitting buffer 205. Still further, the allocation radio
resource setting unit 204 has a function of determining whether or
not to set radio resources whose use is limited by the macro base
station 100-1 using the calculated delay index of the pico base
station 100-1 and the calculated delay index and load index of the
macro base station 200-1, and notifying the pico base station 100-1
of a determination result referring to a surrounding base station
list managed by the base station operating unit 201.
[0059] In the present embodiment, the radio resources whose use is
limited are subframes of the macro base station 200-1, and
subframes whose use is limited are ABSs. In the present embodiment,
as illustrated in FIG. 3, ABSs are set at a cycle of eight
subframes. Hence, an ABS ratio (R_abs) is calculated using
subframes set in 1/8 units. Further, a numerical value in each
subframe in FIG. 3 represents an ABS setting order. As illustrated
in FIG. 3, when R_abs takes 2/8, the allocation radio resource
setting unit 204 sets head two subframes as ABSs.
[0060] Further, the allocation radio resource setting unit 204 does
not set an ABS when radio resources whose use is limited are not
set. Furthermore, the allocation radio resource setting unit 204
uses ABS setting information to notify a determination result. In
the ABS setting information, ABSs set by the macro base station
200-1 and an ABS ratio with respect to all subframes are described.
As disclosed in Non-Patent Literature 4 (3GPP TS 36.423 V10.3.0
(2011-09), 3GPP TSG RAN E-UTRAN X2AP, p. 72, September 2011), in
the ABS setting information, ABS patterns indicating that an ABS is
1 and a Non-ABS is 0 are described.
[0061] The transmitting buffer 205 has the same function as that of
the transmitting buffer 105 of the pico base station 100-1 and
therefore will not be described.
[0062] The scheduler 206 has a function of determining transmission
power, a frequency band and a MCS Index allocated per terminal
300-P, based on a size of transmission data accumulated in the
transmitting buffer 205 and addressed to each terminal 300-P, the
ABS setting information set by the allocation radio resource
setting unit 204 and the CSI reported from each terminal 300-P, and
transmitting data through the base station operating unit 101.
[0063] FIG. 4 is a block diagram illustrating a function of the
terminal 300-P1-1 in the wireless communication system 10. Although
not illustrated in FIG. 4, the functions of the terminal 300-P1-1
are the same as functions of the terminal 300-P1-2, the terminal
300-P2-1, the terminal 300-P2-2, the terminal 300-M1-1 and the
terminal 300-M1-2. The terminal 300-P1-1 includes a terminal
operating unit 301 and a channel quality measuring unit 302.
[0064] The terminal operating unit 301 has a function of
transmitting and receiving radio signals to and from the pico base
station 100-1 which is being connected with the terminal 300-P1-1
(communication link is established). The function of the terminal
operating unit 301 is a known function of a general wireless
communication system, and therefore will not be described.
[0065] The channel quality measuring unit 302 has a function of
measuring channel quality with respect to a reference signal, and
transmitting information of the measured channel quality to the
pico base station 100-1. In the present embodiment, the channel
quality is a CQI calculated from RSRP (Reference Signal Received
Power) and a SINR (Signal To Interference and Noise Ratio) with
respect to the reference signal of the pico base station 100-1. The
RSRP is reception power of the reference signal, and is used as a
reference value of cell selection or handover in the present
embodiment.
[0066] [Explanation of Operation]
[0067] Next, an operation of the above wireless communication
system 10 will be described with reference to FIGS. 5A and 5B.
FIGS. 5A and 5B illustrate operation procedures in which the
allocation radio resource setting unit 204 of the macro base
station 200-1 sets radio resources whose use is limited by the
macro base station 200-1. The allocation radio resource setting
unit 204 executes the operations illustrated in FIGS. 5A and 5B at
each cycle at which the load measuring unit 203 measures a PRB use
ratio.
[0068] First, the allocation radio resource setting unit 204
calculates a delay index of the pico base station 100-1. The delay
time and the PRB use ratio are correlated, and therefore the
allocation radio resource setting unit 204 calculates a delay index
D_pico of the pico base station 100-1 according to equation 1 (step
S101). In equation 1, U_pico represents the PRB use ratio of the
pico base station 100-1 notified from the pico base station
100-1.
[Mathematical 1]
D_pico=U_pico (1)
[0069] Next, the allocation radio resource setting unit 204
determines whether or not a current ABS ratio R_abs of the macro
base station 200-1 is larger than 0 (step S102).
[0070] When R_abs is larger than 0 (Step S102, Yes), the allocation
radio resource setting unit 204 calculates a delay index D_macro of
the macro base station 200-1 which has set radio resources whose
use is limited, according to equation 2 (step S104). In equation 2,
U_macro represents the PRB use ratio of the macro base station
200-1 measured by the load measuring unit 203, and w represents a
weight coefficient. It is assumed that, in case where the macro
base station 200-1 has set radio resources whose use is limited, a
delay time becomes longer as R_abs becomes larger. In the present
embodiment, the weight coefficient w is 1. However, the weight
coefficient w may be set according to the number of terminals
simultaneously connected with the macro base station 200-1 or
channel quality of a terminal. It is assumed that, when, for
example, the number of simultaneously connected terminals before
ABSs are set is great, the weight coefficient is set to a value
larger than 1, and a delay index further increases. This is because
a transmission rate of a terminal lowers when ABSs are set, and
therefore a window size of a TCP hardly expands and a transmission
delay rapidly increases. Further, it is assumed that, when, for
example, ABSs are set and improvement of channel quality in
Non-ABSs can be expected, the weight coefficient is set to a value
smaller than 1, and a delay index does not increase so much. This
is because channel quality in the Non-ABSs improves, and therefore
transmission rates of transmission subframes improve.
[Mathematical 2]
D_macro=w.times.{U_macro/(1-R_abs)} (2)
[0071] Meanwhile, when R_abs is 0 (step S102, No), the allocation
radio resource setting unit 204 sets R_abs to R_abs_ini (step
S103), and moves to step S104. R_abs_ini is an initial value of an
ABS ratio, and the initial value is a minimum value R_min of the
ABS ratio and is set to 1/8 in the present embodiment.
[0072] Next, the allocation radio resource setting unit 204
calculates a relative delay index .DELTA.D of the pico base station
100-1 according to equation 3 (step S105).
[Mathematical 3]
.DELTA.D=D_pico-D.sub.-- (3)
[0073] Next, the allocation radio resource setting unit 204
determines whether or not the calculated relative delay index
.DELTA.D is larger than a required value .DELTA._Thr_max (step S
106).
[0074] When the relative delay index .DELTA.D is larger than the
required value .DELTA._Thr_max (step S106, Yes), the allocation
radio resource setting unit 204 determines that, in case of the
current ABS ratio R_abs, a delay time of the pico terminal 300-P1
with respect to the delay time of the macro terminal 300-M1 in case
where the macro base station 200-1 has set radio resources whose
use is limited is too large, and updates the ABS ratio R_abs
according to equation 4 (step S107). In equation 4, R_step is an
update step size of the ABS ratio R_abs, and takes 1/8 in the
present embodiment. Further, R_max represents an upper limit value
of the settable ABS ratio, and takes 7/8 in the present
embodiment.
[Mathematical 4]
R_abs=MIN[R_max, R_abs+R_step] (4)
[0075] Next, the allocation radio resource setting unit 204
recalculates the delay index D_macro of the macro base station
200-1 which has set the radio resources whose use is limited using
the updated ABS ratio R_abs, according to equation 2 (step S108),
and recalculates the relative delay index .DELTA.D of the pico base
station 100-1, too, according to equation 3 (step S109).
[0076] Next, the allocation radio resource setting unit 204
determines whether or not the recalculated relative delay index
.DELTA.D is a required value .DELTA._Thr or more (step S110).
[0077] When the recalculated relative delay index .DELTA.D is the
required value .DELTA._Thr or more (step S110, Yes), the allocation
radio resource setting unit 204 determines that, in case of the
updated ABS ratio R_abs, an increase in a delay time of the
terminal 300-M1 in case where the macro base station 200-1 has set
the radio resources whose use is limited is not great, and
calculates the number of transmitted bits TB (Transmitted
Bits)_macro per RB of the macro base station 200-1 which is
required to calculate a load index L_macro of the macro base
station 200-1, according to equation 5 (step S111). In equation 5,
U_macro is a PRB use ratio of the macro base station 200-1 measured
by the load measuring unit 203. BS_present is a buffer size which
is being buffered in the transmitting buffer 205 in a current
subframe. BS_past is a buffer size which has been buffered in a
subframe a predetermined time T_subframe before from a current
subframe. .DELTA.S is a data size which has arrived at the
transmitting buffer 205 in this predetermined time T_subframe.
[0078] On a right side of equation 5, a numerator represents a
total size of data whose transmission has been completed by the
macro base station 200-1 in the predetermined time T_subframe, and
a denominator represents a total number of PRBs which the macro
base station 200-1 has used to transmit data in the predetermined
time T_subframe. N_PRB represents the number of allocatable PRBs
per subframe, and T_subframe represents a notification cycle of a
PRB use ratio.
[Mathematical 5]
TB_macro [bits/Sub
frame]=(BS_past+.DELTA.S-BS_present)/(U_macro.times.N.sub.--PRB.times.T_s-
ubframe) (5)
[0079] Next, the allocation radio resource setting unit 204
calculates the load index L_macro of the macro base station 200-1
using calculated TB_macro according to equation 6A (step S112).
According to equation 6A, it is possible to calculate as a load
index of the macro base station 200-1 an estimated PRB use ratio
which is a ratio of a total number of PRBs required until
transmission of data which is being buffered in a transmitting
buffer is finished, with respect to the total number of PRBs which
can be used until the predetermined time T_subframe passes from a
current time.
[Mathematical 6]
L_macro=MIN[1.0,
(BS_present/TB_macro)/(N.sub.--PRB.times.T_subframe)] (6A)
[0080] Next, the allocation radio resource setting unit 204
determines whether or not the calculated load index L_macro of the
macro base station 200-1 is a threshold L_Thr or more (step
S113).
[0081] When the calculated load index L_macro is the threshold
L_Thr or more (step S113, Yes), the allocation radio resource
setting unit 204 determines that a transmission probability of the
macro base station 200-1 is high, and a probability that a pico
terminal 300-P1 receives an interference from the macro base
station 200-1 is high, too, and determines whether or not the
updated ABS ratio is the same as a current setting value (step
S114).
[0082] When the updated ABS ratio is the same as the current
setting value (step S114, Yes), the allocation radio resource
setting unit 204 finishes the processing in FIG. 5. Meanwhile, when
the updated ABS ratio is different from the current setting value
(step S114, No), the allocation radio resource setting unit 204
sets ABSs at the updated ABS ratio, and notifies the pico base
station 100-1 of setting information of the set ABSs. Subsequently,
the allocation radio resource setting unit 204 finishes the
processing in FIG. 5.
[0083] Meanwhile, when the relative delay index .DELTA.D is the
required value .DELTA._Thr_max or less (step S106, No), the
allocation radio resource setting unit 204 determines whether or
not the relative delay index .DELTA.D is less than a required value
.DELTA._Thr_min (<.DELTA._Thr_max) (step S116). When the
relative delay index .DELTA.D is the required value .DELTA._Thr_min
or more (step S116, No), the allocation radio resource setting unit
204 moves to step S108 without changing the ABS ratio R_abs.
Meanwhile, when the relative delay index .DELTA.D is less than the
required value .DELTA._Thr_min (step S116, Yes), the allocation
radio resource setting unit 204 determines that, in case of the
current ABS ratio R_abs, an increase in a delay time of the
terminal 300-M1 in case where the macro base station 200-1 has set
the radio resources whose use is limited is great, and updates the
ABS ratio R_abs according to equation 7 (step S117).
[Mathematical 7]
R_abs=R_abs-R_step (7)
[0084] Subsequently, the allocation radio resource setting unit 204
determines whether or not the updated ABS ratio R_abs is the
minimum value R_min or more (step S118).
[0085] When the updated ABS ratio R_abs is the minimum value R_min
or more (step S118, Yes), the allocation radio resource setting
unit 204 moves to step S108. Meanwhile, when the updated ABS ratio
R_abs is less than the minimum value R_min (step S118, No), the
allocation radio resource setting unit 204 determines that the
macro base station 200-1 cannot set ABSs, and determines whether or
not the macro base station 200-1 has already set the ABSs (step
S119). In case where the macro base station 200-1 has set the ABSs
(step S119, Yes), the allocation radio resource setting unit 204
cancels the set ABSs, and notifies the pico base station 100-1 of
the ABS setting information (step S120). Subsequently, the
allocation radio resource setting unit 204 finishes the processing
in FIG. 6. Meanwhile, in case where the macro base station 200-1
has not set the ABSs (step S119, No), the allocation radio resource
setting unit 204 finishes the processing in FIG. 5.
[0086] Further, when the recalculated relative delay index .DELTA.D
is less than the required value .DELTA._Thr (step S110, No), the
allocation radio resource setting unit 204 determines that, in case
of the updated ABS ratio R_abs, an increase in the delay time of
the terminal 300-M1 in case where the macro base station 200-1 has
set radio resources whose use is limited is great, and moves to
step S119.
[0087] Furthermore, when the load index L_macro of the macro base
station 200-1 is less than the threshold L_Thr (step S113, No), the
allocation radio resource setting unit 204 determines that a
transmission probability of the macro base station 200-1 is low,
and a probability that a pico terminal 300-P1 receives an
interference from the macro base station 200-1 is low, too, and
moves to step S119.
[0088] As described above, according to the pico base station 100-1
and the macro base station 200-1 according to the first embodiment
of the present invention, when a load of the macro base station
200-1 is great, the macro base station 200-1 sets the radio
resources whose use is limited such that a relative delay index of
the pico base station 100-1 settles in a predetermined range.
Consequently, it is possible to avoid deterioration of a 5% value
of throughputs of all terminals due to deterioration of a
throughput of the macro terminal 300-M, and improve fairness
between throughputs of all communication terminals 300 including
terminals of the macro base station 200 and the pico base station
100.
[0089] The present invention has been described above with
reference to the above embodiment. However, the present invention
is not limited to the above embodiment. Various changes which one
of ordinary skill in the art can understand can be applied to the
configurations and the details of the present invention within the
scope of the present invention.
[0090] For example, as disclosed in Non-Patent Literature 5 (3GPP
TS 36.314 V10.2.0 (2011-09), 3GPP TSG RAN E-UTRAN Layer
2-Measurement, p. 9, p. 11, p. 15, September 2011), the allocation
radio resource setting unit 204 can also calculate a delay index
using the number of Active UEs, a delay time or a throughput per
terminal instead of a PRB use ratio. The throughput per terminal
is, for example, a size of data whose transmission to a terminal
has succeeded during a connection time of the terminal. In
addition, there are a method of directly notifying between base
stations of these pieces of information and a method of connecting
an OAM server onto the communication line NW and notifying these
pieces of information through the OAM server to calculate a delay
index using the number of Active UEs, the delay time or the
throughput. In case of the latter, the OAM server has a function of
counting the number of Active UEs, a delay time or a throughput per
terminal from each pico base station 100 and each macro base
station 200 connected to the communication line NW.
[0091] Further, the allocation radio resource setting unit 204 may
calculate as a relative delay index of the pico base station 100-1
a ratio of a delay index of the macro base station 200-1 in case
where radio resources whose use is limited have been set, with
respect to a delay index of the pico base station 100-1 instead of
calculating a difference value between a delay index of the pico
base station 100-1 and a delay index of the macro base station
200-1 in case where the radio resources whose use is limited have
been set.
[0092] Furthermore, the allocation radio resource setting unit 204
may also use a PRB use ratio as a load index of the macro base
station 200-1 without using the number of transmitted bits TB_macro
per RB of the macro base station 200-1. Alternatively, the
allocation radio resource setting unit 204 may also use the number
of Active UEs as the load index of the macro base station
200-1.
[0093] Further, the allocation radio resource setting unit 204 can
also determine whether or not the macro base station 200-1 sets
radio resources whose use is limited, without calculating the load
index of the macro base station 200-1. In this case, it is possible
to skip step S114 to step S116 in FIG. 4 and, consequently, reduce
a processing load of the macro base section 200-1 compared to the
present embodiment.
[0094] Further, the present invention is also applicable even when
a plurality of pico base stations are located in a communication
area of a macro base station. In this case, the allocation radio
resource setting unit 204 uses an average value of delay indices
calculated per pico base station in the communication area or a
predetermined value of a cumulative distribution as a delay index
of the pico base station 100-1.
[0095] Further, it is also possible to calculate the load index
L_macro of the macro base station 200-1 according to equation 6B.
In equation 6B, .DELTA.S_ave represents an average value of data
sizes which arrive at the transmitting buffer 205 of the macro base
station 200-1 in the predetermined time T_subframe. According to
equation 6B, it is possible to calculate as a load index of the
macro base station 200-1 an estimated PRB use ratio which is a
ratio of a total number of PRBs required until transmission of data
which is being buffered in a transmitting buffer and data produced
in the predetermined time T_subframe are finished, with respect to
the total number of PRBs which can be used until the predetermined
time T_subframe passes from a current time.
[Mathematical 8]
L_macro=MIN[1.0,{(BS_present+.DELTA.S_ave)/TB_macro}/(N.sub.--PRB.times.-
T_subframe)] (6B)
[0096] In addition, .DELTA.S_ave is updated according to equation 8
immediately before equation 6B is calculated. In equation 8,
.DELTA.S_ave_previous represents an average value of data sizes
before an update, and .omega. represents a weight coefficient.
[Mathematical 9]
.DELTA.S_ave=.omega..times..DELTA.S+(1-.omega.).times..DELTA.S_ave_previ-
ous (8)
[0097] The above changes can be made likewise in the subsequent
embodiments, too.
Second Embodiment
ABS Ratio is Directly Calculated Using Load
[0098] Next, the second embodiment of the present invention will be
described in detail with reference to the drawings. Differences
include that, while a ratio of radio resources whose use is limited
is updated in predetermined step units according to a relative
delay index of a pico base station 100-1 in the present embodiment,
a ratio of radio resources whose use is limited is directly
calculated using a relative delay index of the pico base station
100-1 in the present embodiment.
[0099] [Explanation of Configuration]
[0100] A pico base station according to the second embodiment is
the same as a pico base station 100 according to the first
embodiment, and therefore will not be described.
[0101] FIG. 6 is a block diagram illustrating functions of each
macro base station 400 according to the second embodiment. The
functions will be described using a macro base station 400-1 as a
macro base station. Although not illustrated in FIG. 6, functions
of a macro base station 400-2 are the same as the functions of the
macro base station 400-1.
[0102] The macro base station 400-1 according to the second
embodiment differs from a macro base station 200-1 according to the
first embodiment in including an allocation radio resource setting
unit 404 instead of an allocation radio resource setting unit 204.
The allocation radio resource setting unit 404 will be described
below.
[0103] The allocation radio resource setting unit 404 has a
function of calculating a ratio of radio resources whose use is
limited using load information notified from the pico base station
100-1 and .a load of the macro base station 400-1 measured by a
load measuring unit 203. Further, the allocation radio resource
setting unit 404 has a function of calculating a delay index for
determining a delay time of a terminal of a pico base station 100-1
and a delay index indicating a delay time of the macro base station
400-1 which has set radio resources whose use is limited,
respectively, using the calculated ratio of radio resources whose
use is limited, the load information notified from the pico base
station 100-1 and a load of the macro base station 400-1 measured
by the load measuring unit 203.
[0104] Furthermore, the allocation radio resource setting unit 404
has a function of calculating a load index of the macro base
station 400-1 according to the same method as that of the
allocation radio resource setting unit 204 according to the first
embodiment. Still further, the allocation radio resource setting
unit 404 has a function of determining whether or not to set radio
resources whose use is limited by the macro base station 400-1
according to the same method as that of the allocation radio
resource setting unit 204 according to the first embodiment, and
notifying the pico base station 100-1 of a determination result
referring to a surrounding base station list managed by a base
station operating unit 201.
[0105] In the present embodiment, radio resources whose use is
limited are subframes of the macro base station 400-1, and
subframes whose use is limited are ABSs. When radio resources whose
use is limited are set, the allocation radio resource setting unit
404 sets ABSs according to a same method as that of the allocation
radio resource setting unit 204 according to the first embodiment
using the calculated ABS ratio. Further, when radio resources whose
use is limited are not set, the allocation radio resource setting
unit 404 does not set ABSs. Furthermore, the allocation radio
resource setting unit 404 uses ABS setting information to notify a
determination result. In the ABS setting information, ABS patterns
indicating that an ABS is 1 and a Non-ABS is 0 are described.
[0106] [Explanation of Operation]
[0107] FIG. 7 illustrates an operation procedure in which the
allocation radio resource setting unit 404 of the macro base
station 400-1 sets radio resources whose use is limited. The
allocation radio resource setting unit 404 executes the operation
illustrated in FIG. 7 at each cycle at which the load measuring
unit 203 measures a PRB use ratio.
[0108] In view of FIG. 7, step S118 in FIG. 5 moves to a step
before step S101. Further, step S102 to step S109 and step S116 and
step S117 in FIG. 5 are omitted, and new step S201 is added. Only
the operation in added step S201 will be described below.
[0109] The allocation radio resource setting unit 404 calculates an
ABS ratio R_abs according to equation 9 using a PRB use ratio
U_pico of the pico base station 100-1 notified from the pico base
station 100-1, and a PRB use ratio U_macro of the macro base
station 400-1 measured by the load measuring unit 203 (step S201).
In equation 9, R_max represents a maximum value of an ABS ratio,
.DELTA.D_target represents a target value of a relative delay index
of the pico base station 100-1, and w represents a weight
coefficient. In the present embodiment, the weight coefficient w
takes 1.0. Still further, FLOOR{t} represents a function of
returning a maximum integer which does not exceed an argument t.
Equation 9 is transformed into an equation of calculating the ABS
ratio R_abs using equation 1 and equation 2 by replacing AD on a
left side of equation 3 with .DELTA.D_target (an equation which is
not yet transformed is provided as equation 10). Consequently,
using equation 9, the allocation radio resource setting unit 404
can calculate R_abs such that the relative delay index .DELTA.D of
the pico base station 100-1 takes the target value
.DELTA.D_target.
[Mathematical 10]
R_abs=MAX[R_max,MIN
[0,FLOOR{.times.(1-w.times.U_macro)/(U_pico-.DELTA.D_target)}/8]]
(9)
[Mathematical 11]
D_target=D_pico-D_macro=U_pico-w.times.{U_macro/(1-R_abs)} (10)
[0110] As described above, according to the pico base station 100-1
and the macro base station 400-1 according to the second embodiment
of the present invention, when a load of the macro base station
400-1 is great, it is possible to directly calculate a ratio of
radio resources whose use is limited such that a relative delay
index of a pico base station 700-1 takes a target value.
Consequently, a time which the ratio of radio resources whose use
is limited takes to converge shortens compared to the first
embodiment of the present invention. Further, the time which the
ratio of the radio resources whose use is limited takes to converge
is short. Consequently, it is possible to improve fairness between
throughputs of all terminals 300 including terminals of the macro
base station 400 and the pico base station 100 in a short time
compared to the first embodiment of the present invention.
[0111] The present invention has been described above with
reference to the above embodiment. However, the present invention
is not limited to the above embodiment. Various changes which one
of ordinary skill in the art can understand can be applied to the
configurations and the details of the present invention within the
scope of the present invention.
[0112] For example, a difference value between a delay index of the
pico base station 100-1 and a delay index of the macro base station
400-1 in case where radio resources whose use is limited have been
set is calculated as a relative delay index of the pico base
station 100-1 in the present embodiment. However, a ratio of the
delay index of the macro base station 400-1 in case where radio
resources whose use is limited have been set, with respect to the
delay index of the pico base station 100-1 may be calculated. In
this case, the allocation radio resource setting unit 204
calculates the ABS ratio R_abs in step S201 according to equation
11. Equation 11 is transformed into an equation of calculating the
ABS ratio R_abs using equation 1 and equation 2 by replacing
.DELTA.D with .DELTA.D_target in an equation of calculating as a
relative delay index AD of the pico base station 100-1 a ratio of a
delay index of the macro base station 200-1 in case where radio
resources whose use is limited have been set, with respect to a
delay index of the pico base station 100-1 (the equation which is
not yet transformed is provided as equation 12). Even when a ratio
of the delay indices is used, it is possible to perform control
such that a relative delay index takes a target value.
Consequently, it is possible to provide the same effect as that
obtained when a difference between delay indices is used.
[Mathematical 12]
R_abs=MAX[R_max,MIN
[0,FLOOR{8.times.(U_pico-w.times.U_macro.times..DELTA.D_target)/U_pico}/8-
]] (11)
[Mathematical 13]
.DELTA.D_target=D_pico/D_macro=U_pico/[w.times.{U_macro/(1-R_abs)}]
(12)
[0113] The above changes can be made likewise in subsequent
embodiments, too.
Third Embodiment
Limitation is Placed on Frequency
[0114] Next, the third embodiment of the present invention will be
described in detail with reference to the drawings. The present
embodiment differs from the second embodiment in changing radio
resources whose use is limited from subframes to PRBs.
[0115] [Explanation of Configuration]
[0116] A pico base station according to the third embodiment is the
same as a pico base station 100 according to the second embodiment,
and therefore will not be described.
[0117] FIG. 8 is a block diagram illustrating functions of each
macro base station 500 according to the third embodiment. The
functions will be described using a macro base station 500-1 as a
macro base station. Although not illustrated in FIG. 8, functions
of a macro base station 500-2 are the same as the functions of the
macro base station 500-1.
[0118] The macro base station 500-1 according to the third
embodiment differs from a macro base station 400-1 according to the
second embodiment in including an allocation radio resource setting
unit 504 instead of an allocation radio resource setting unit 404.
The allocation radio resource setting unit 504 will be described
below.
[0119] The allocation radio resource setting unit 504 has the same
function as that of the allocation radio resource setting unit 404
according to the second embodiment. Meanwhile, radio resources
whose use is limited are different from those of the allocation
radio resource setting unit 404.
[0120] In the present embodiment, radio resources whose use is
limited are PRBs of the macro base station 500-1, and, when it is
determined that radio resources whose use is limited are set, PRBs
which are not allocated to terminals are set in order from a PRB
whose index is the smallest at a calculated ratio of radio
resources whose use is limited.
[0121] [Explanation of Operation]
[0122] FIG. 10 illustrates an operation procedure in which the
allocation radio resource setting unit 504 of the macro base
station 500-1 sets radio resources whose use is limited. The
allocation radio resource setting unit 504 executes the operation
illustrated in FIG. 10 at each cycle at which a load measuring unit
203 measures a PRB use ratio.
[0123] In view of FIG. 10, step S201 in FIG. 7 is changed to step
S301, step S118 in FIG. 7 is changed to step S302 and step S108 in
FIG. 7 is changed to step S303, respectively. Further, steps S114,
S115, S119 and S120 in FIG. 7 are omitted, and step S304 to step
S307 are added. Only the operations in step S301 to step S307 will
be described below.
[0124] The allocation radio resource setting unit 504 calculates
the number of PRBs N_prior which are not allocated to terminals
according to equation 7 using a PRB use ratio U_pico of a pico base
station 100-1 notified from a pico base station 100-1 and a PRB use
ratio U_macro of the macro base station 500-1 measured by the load
measuring unit 203. In equation 7, w represents a weight
coefficient, and takes 1.0 in the present embodiment. The
allocation radio resource setting unit 504 can calculate N_prior
such that a delay target index .DELTA.D of the pico base station
100-1 takes a target value .DELTA.D_target using equation 7.
[Mathematical 14]
N_prior=MAX[N.sub.--PRB,MIN
[0,FLOOR{N_PRB.times.(1-w.times.macro)/(U_pico-.DELTA.D_target)}]]
(13)
[0125] Next, the allocation radio resource setting unit 504
determines whether or not calculated N_prior is a minimum value
N_min or more (step S302). In the present embodiment, the minimum
value N_min takes 1. When calculated N_prior is the minimum value
N_min or more (step S302, Yes), the allocation radio resource
setting unit 504 calculates a delay index D_pico of the pico base
station 100-1 according to equation 1 (step S101), and then
calculates a delay index D_macro in case where the macro base
station 500-1 has set radio resources whose use is limited, using
calculated N_prior according to equation 14 (step S303). In
equation 14, w represents a weight coefficient, and takes 1.0 in
the present embodiment.
[Mathematical 15]
D_macro=w.times.[U_macro/{1-(N_prior/N.sub.--PRB)}] (14)
[0126] Further, when determining that a load index L_macro of the
macro base station 500-1 calculated in step S115 is a threshold
L_Thr or more (step S113, Yes), the allocation radio resource
setting unit 504 determines whether or not calculated N_prior is
the same as a current setting value (step S304).
[0127] When calculated N_prior is the same as the current setting
value (step S304, Yes), the allocation radio resource setting unit
504 finishes the processing in FIG. 10. Meanwhile, when calculated
N_prior is different from the current setting value (step S304,
No), the allocation radio resource setting unit 504 sets PRBs which
are not allocated to terminals using calculated N_prior (step
S306). Subsequently, the allocation radio resource setting unit 504
finishes the processing in FIG. 10.
[0128] Further, when determining that the load index L_macro of the
macro base station 500-1 calculated in step S112 is less than the
threshold L_Thr (step S113, No), the allocation radio resource
setting unit 504 determines whether or not PRBs which are not
allocated to terminals are set (step S306).
[0129] When PRBs which are not allocated to terminals are set (step
S306, Yes), the allocation radio resource setting unit 504 cancels
the set PRBs which are not allocated to the terminals (step S307).
Subsequently, the allocation radio resource setting unit 504
finishes the processing in FIG. 10. Meanwhile, when PRBs which are
not allocated to terminals are not set (step S308, No), the
allocation radio resource setting unit 504 finishes the processing
in FIG. 10. Further, when calculated N_prior is less than the
minimum value N_min (step S302, No), the allocation radio resource
setting unit 504 moves to step S306.
[0130] The present invention has been described above with
reference to the above embodiment. However, the present invention
is not limited to the above embodiment. Various changes which one
of ordinary skill in the art can understand can be applied to the
configurations and the details of the present invention within the
scope of the present invention.
[0131] For example, the allocation radio resource setting unit 504
can also update the number of RBs which are priority bands of the
pico base station 100-1 such that a difference value between a
delay index of the pico base station 100-1 and a delay index of the
macro base station 500-1 which has set radio resources whose use is
limited settles in a predetermined range according to the same
method as that in the first embodiment. The above changes can be
made likewise in the subsequent embodiments, too.
Fourth Embodiment
Pico Base Station Calculates ABS Ratio, and Notifies Macro Base
Station of ABS Ratio
[0132] Next, the fourth embodiment of the present invention will be
described in detail with reference to the drawings. Differences
include that, while a macro base station sets a ratio of radio
resources whose use is limited and notifies a pico base station of
this setting information in the second embodiment, a pico base
station requests radio resources whose use is limited by the macro
base station, and the macro base station sets radio resources whose
use is limited according to the request from the pico base station
in the present embodiment.
[0133] [Explanation of Configuration]
[0134] FIG. 11 is a block diagram illustrating functions of each
pico base station 600 and each macro base station 700 according to
the fourth embodiment. The functions will be described using a pico
base station 600-1 as a pico base station and a macro base station
700-1 as a macro base station. Although not illustrated in FIG. 11,
functions of a pico base station 600-2 are the same as the
functions of the pico base station 600-1. Similarly, functions of a
macro base station 700-2 are the same as the functions of the macro
base station 700-1.
[0135] The pico base station 600-1 according to the fourth
embodiment differs from a pico base station 100-1 according to the
second embodiment in additionally including a priority resource
requesting unit 604. Further, the macro base station 700-1
according to the fourth embodiment differs from a macro base
station 400-1 according to the second embodiment in including an
allocation radio resource setting unit 704 instead of an allocation
radio resource setting unit 204. The priority resource requesting
unit 606 and the allocation radio resource setting unit 704 will be
described below.
[0136] The priority resource requesting unit 606 has a function of
calculating a ratio of radio resources whose use is limited using a
load of the pico base station 600-1 measured by a load measuring
unit 103 and load information notified from the macro base station
700-1. Further, the priority resource requesting unit 606 has a
function of calculating a delay index for determining a delay time
of a terminal of the pico base station 600-1 and a delay index
indicating a delay time of the macro base station 700-1 in case
where radio resources whose use is limited have been set,
respectively, using the calculated ratio of radio resources whose
use is limited, a load of the pico base station 600-1 measured by
the load measuring unit 103, and the load information notified from
the macro base station 700-1. Furthermore, the priority resource
requesting unit 606 has a function of calculating the load index of
the macro base station 400-1 using the load information notified
from the macro base station 700-1. Still further, the priority
resource requesting unit 606 has a function of determining whether
or not to request priority resources of the pico base station
600-1, to the macro base station based on the calculated delay
index of the pico base station 600-1 and the calculated delay index
and load index of the macro base station 700-1, and has a function
of notifying the macro base station 700-1 of a determination result
referring to a surrounding base station list managed by a base
station operating unit 101.
[0137] In the present embodiment, radio resources whose use is
limited are ABSs of the macro base station 700-1, and ABS setting
information is used to notify a determination result. The ABS
setting information is generally used to notify that a base station
which has set ABSs has set ABSs to surrounding base stations.
However, a pico base station uses ABS setting information to
request a macro base station to set ABSs in the present embodiment.
In the ABS setting information, ABS patterns indicating that an ABS
is 1 and a Non-ABS is 0 are described. When requesting priority
resources to the macro base station 700-1, the priority resource
requesting unit 606 describes a request for priority resources in
ABS setting information for setting ABSs according to the same
method as that of the allocation radio resource setting unit 204
according to the first embodiment using the calculated ABS ratio.
Further, when not requesting priority resources to the macro base
station 700-1, the priority resource requesting unit 606 describes
information indicating that all subframes are Non-ABSs, in the ABS
setting information.
[0138] The allocation radio resource setting unit 704 has a
function of setting radio resources whose use is limited according
to the ABS setting information notified from the pico base station
600-1. In the present embodiment, the radio resources whose use is
limited are subframes of the macro base station 200-1, and
subframes whose use is limited are ABSs. When setting radio
resources whose use is limited, the allocation radio resource
setting unit 704 sets ABSs according to a pattern instructed by the
pico base station 600-1. Further, when not setting radio resources
whose use is limited, the allocation radio resource setting unit
704 does not set ABSs.
[0139] [Explanation of Operation]
[0140] FIG. 12 illustrates an operation procedure in which the
priority resource requesting unit 606 of the pico base station
600-1 determines whether or not to request the macro base station
700-1 to set radio resources whose use is limited. The priority
resource requesting unit 606 executes the operation illustrated in
FIG. 12 at each cycle at which the load measuring unit 103 measures
a PRB use ratio.
[0141] In FIG. 12, step S111 and step S112 in FIG. 7 are changed to
step S401. Further, steps S114, S115, S119 and S120 in FIG. 7 are
omitted, and step S402 and step S403 are added. Only operations
subsequent to step S401 will be described below.
[0142] The priority resource requesting unit 606 calculates a load
index L_macro of the macro base station 700-1 according to equation
15 using the PRB use ratio notified from the macro base station
700-1 (step S401).
[Mathematical 16]
L_macro=U_macro (15)
[0143] Next, the priority resource requesting unit 606 determines
whether or not the calculated load index L_macro of the macro base
station 700-1 is a threshold L_Thr or more (step S116).
[0144] When the calculated load index L_macro is the threshold
L_Thr or more (step S113, Yes), the priority resource requesting
unit 606 determines that a transmission probability of the macro
base station 700-1 is high, and a probability that a pico terminal
300-P1 receives an interference from the macro base station 700-1
is high, too, and notifies the macro base station 700-1 of ABS
setting information for setting ABSs set using an ABS ratio R_abs
calculated in step S201 (step S402). Subsequently, the priority
resource requesting unit 606 finishes the processing in FIG.
10.
[0145] When the calculated load index L_macro is less than the
threshold L_Thr (step S116, No), the priority resource requesting
unit 606 determines that a transmission probability of the macro
base station 700-1 is low, and a probability that a pico terminal
300-P1 receives an interference from the macro base station 700-1
is low, too, and notifies the macro base station 700-1 of the ABS
setting information indicating that all subframes are Non-ABSs.
Subsequently, the priority resource requesting unit 606 finishes
the processing in FIG. 10.
[0146] FIG. 13 illustrates an operation procedure in which the
allocation radio resource setting unit 704 of the macro base
station 700-1 sets radio resources whose use is limited according
to ABS setting information from the pico base station 600-1. The
allocation radio resource setting unit 704 executes the operation
illustrated in FIG. 13 every time the allocation radio resource
setting unit 704 receives RNTP from the pico base station
600-1.
[0147] First, the allocation radio resource setting unit 704
determines whether or not the ABS ratio R_abs described in the ABS
setting information notified from the pico base station 600-1 to
the macro base station 700-1 is larger than 0 (step S501).
[0148] When the ABS ratio R_abs is larger than 0 (step S501, Yes),
the allocation radio resource setting unit 704 determines whether
or not R_abs is the same as a current setting value (step
S114).
[0149] When R_abs is the same as the current setting value (step
S114, Yes), the allocation radio resource setting unit 704 finishes
the processing in FIG. 13. Meanwhile, when R_abs is different from
the current setting value (step S114, No), the allocation radio
resource setting unit 704 sets ABSs at R_abs (step S502).
Subsequently, the allocation radio resource setting unit 704
finishes the processing in FIG. 13.
[0150] Further, when the ABS ratio R_abs is 0 (step S501, No), the
allocation radio resource setting unit 704 determines whether or
not the macro base station 700-1 has already set ABSs (step S119).
In case where the macro base station 700-1 has already set ABSs
(step S119, Yes), the allocation radio resource setting unit 704
cancels the set ABSs (step S503). Subsequently, the allocation
radio resource setting unit 704 finishes the processing in FIG. 13.
Meanwhile, in case where the macro base station 700-1 has not set
ABSs (step S119, No), the allocation radio resource setting unit
704 finishes the processing in FIG. 13.
[0151] The present invention has been described above with
reference to the above embodiment. However, the present invention
is not limited to the above embodiment. Various changes which one
of ordinary skill in the art can understand can be applied to the
configurations and the details of the present invention within the
scope of the present invention.
[0152] For example, the allocation radio resource setting unit 704
cancels a limitation placed on set radio resources whose use is
limited when ABS setting information indicating that the ABS ratio
is 0 is notified from the pico base station 600-1. However, a
limitation on radio resources may be canceled when a predetermined
time passes after setting the radio resources whose use is limited
is started. In this case, the priority resource requesting unit 606
can skip the processing in step S403. Consequently, it is possible
to reduce a processing load of the pico base station 600-1 compared
to the present embodiment. Further, the pico base station 600-1
only needs to notify ABS setting information in case where the
macro base station 700-1 sets radio resources whose use is limited.
Consequently, it is possible to suppress a signaling amount between
base stations through a communication line NW compared to the
present embodiment.
[0153] Furthermore, ABSs are set by setting radio resources whose
use is limited in the present embodiment. However, similar to the
third embodiment, it is also possible to set to each terminal
300-M1 an allocatable band as a band formed by excluding a priority
band of the pico base station 600-1 from a system band. In this
case, the priority resource requesting unit 606 calculates the
number of RBs which are priority bands of the pico base station
600-1 according to the same method as that of an allocation radio
resource setting unit 504 of a macro base station 500-1 according
to the third embodiment, and notifies the macro base station 700-1
of a calculation result. RNTP is used to notify a calculation
result. 1 is set to RNTP in a RB (Resource block) which is
requested as a priority band, and 0 is set to RNTP in a RB which is
not requested as a priority band. A RB represents a frequency block
which is a radio band allocation unit.
[0154] Further, the present invention is also applicable even when
a plurality of pico base stations are located in a communication
area of a macro base station. In this case, the allocation radio
resource setting unit 704 calculates a rate of the number of pico
base stations which have notified ABS setting information
indicating that an ABS ratio is larger than 0, with respect to a
total number of base stations in a communication area, and sets
ABSs according to ABS setting information of the lowest ABS ratio
among ABS ratios which are larger than 0 only when the rates are a
threshold of the rates or more. Alternatively, the allocation radio
resource setting unit 704 can also set ABSs to subframes whose ABSs
overlap among a plurality of pieces of ABS setting information.
[0155] In addition, the present invention is not limited to the
above embodiments, and can be optionally changed without departing
from the spirit of the present invention.
[0156] Although the present invention has been described as a
hardware configuration in the above embodiments, the present
invention is not limited to these. The present invention can also
be realized by causing a CPU (Central Processing Unit) to execute a
computer program to perform the processing in a terminal or a base
station. In this case, the computer program can be supplied to the
computer by being stored using various types of non-transitory
computer readable media. The non-transitory computer readable media
include various types of tangible storage media. The non-transitory
computer readable media include, for example, magnetic recording
media (e.g. flexible disks, magnetic tapes and hard disk drives),
magnetooptical recording media (e.g. magnetooptical disks), CD-ROMs
(Read Only Memory), CD-Rs, CD-R/Ws, and semiconductor memories
(e.g. mask ROMs, PROMs (Programmable ROM), EPROMs (Erasable PROM),
flash ROMs and RAMs (Random Access Memory)). Further, the program
may be supplied to the computer using various types of transitory
computer readable media. The transitory computer readable media
include, for example, electric signals, optical signals and
electromagnetic waves. The transitory computer readable media can
supply the program to the computer using wired communication
channels such as electric wires and optical fibers or wireless
communication channels.
[0157] Although the present invention has been described above with
reference to the embodiments, the present invention is by no means
limited to the above embodiments. Various changes which one of
ordinary skill in the art can understand can be applied to the
configurations and the details of the present invention within the
scope of the invention.
[0158] This application claims priority to Japanese Patent
Application No. 2012-246962 filed on Nov. 9, 2012, the entire
contents of which are incorporated by reference herein.
REFERENCE SIGNS LIST
[0159] 10 RADIO COMMUNICATION SYSTEM
[0160] 100-1, 100-2, 600-1 PICO BASE STATION
[0161] 200-1, 200-2, 400-1, 500-1, 700-1 MACRO BASE STATION
[0162] 300-P1-1, 300-P1-2, 300-P2-1, 300-P2-2, 300-M1-1, 300-M1-2,
300-M2-1, 300-M2-2 TERMINAL
[0163] 101, 201 BASE STATION OPERATING UNIT
[0164] 102, 202 REFERENCE SIGNAL GENERATING UNIT
[0165] 103, 203 LOAD MEASURING UNIT
[0166] 104, 205 TRANSMITTING BUFFER
[0167] 105, 206 SCHEDULER
[0168] 606 PRIORITY RESOURCE REQUESTING UNIT
[0169] 204, 404, 504, 704 ALLOCATION RADIO RESOURCE SETTING
UNIT
[0170] 301 TERMINAL OPERATING UNIT
[0171] 302 CHANNEL QUALITY MEASURING UNIT
* * * * *